The present invention relates generally to a method of making articles containing cellulosic fibers, such as wood pulp, and synthetic fibers. More specifically, the invention relates to an apparatus for and a method of continuously feeding and blending cellulosic and synthetic fibers in a metered fashion to create a homogeneous blend which may be air-layed and thermobonded, as well as to an article formed in this manner.
Although methods of blending cellulosic and synthetic fibers and other fibers are known, these prior methods, and articles produced by such methods, suffer from a number of disadvantages. Uncontrolled blending of synthetic fibers with cellulosic fibers results in an inconsistent blend producing variances in the properties of a given article, as well as variances between articles. For example, stratification of the air-layed blend, where the cellulosic fibers are layered separately from the synthetic fibers, may result in nonuniform heat bonding of a core formed by the cellulosic and synthetic fibers. Therefore, strict quality control and product uniformity in such areas as basis weight, and strength are hampered by these earlier known methods.
Furthermore, the known methods of blending fibers suffer from problems associated with producing a wide variety of closely controlled blend ratios of cellulosic to synthetic fibers. Moreover, these methods experience problems when simultaneously blending several fibers of different lengths, deniers or superabsorbent polymers (SAP). Additionally, earlier methods of blending known to the inventors cannot be effectively controlled so as to provide a resulting article with either high X-Y tensile strength, high Z-tensile strength, or a combination thereof.
Two known earlier fiber blending systems are known as a Dan Web Former and a M & J Web Former. The Dan and M & J Web Formers are modifications of an earlier system, known as the Kroyer Process, which dealt with a method of air-laying dry cellulose fibers.
The Dan Web Former has a pulp preparation line preparing wood pulp fibers, and a synthetic fiber preparation line preparing synthetic fibers, with the wood pulp fibers and synthetic fibers being mixed within a distribution head drum. The pulp preparation line includes a hammermill which receives and fiberizes wood pulp sheets in a fiberizing chamber. The hammermill has a fiberization screen at the exit of the fiberization chamber for determining the degree of wood pulp fiberization, that is the size of the wood pulp fibers. The wood pulp fibers are delivered through a blower from the hammermill to the interior of the distribution head drum.
The Dan Web Former synthetic fiber preparation line has a fiber opening system which receives and opens synthetic fiber bales. The opened synthetic fibers are metered by weight, not volume, and then are forced with another blower to the interior of the distribution head drum. The distribution head drum has a plurality of apertures extending through the drum wall. The drum is rotated about its longitudinal axis, and has several cylindrical combers in the drum which aid in mixing the fibers and pushing them through the holes in the drum wall. The drum is supported from below by at least two rollers, which serve to rotate the drum. The drum is surrounded by a shroud and a foraminous conveyer belt passes through the shroud beneath the drum. A vacuum may be pulled within the shroud to draw the fibers onto the foraminous conveyer belt.
The Dan Web Former distribution head drum serves as a tumble mixer and a sifter, with the synthetic and wood pulp fibers eventually sifting through the holes in the drum wall. In commercial practice, with drum wall holes 1/4 inch in diameter, the length of fibers which fall through the distribution head are not longer than 1/4 inch. If the drum wall holes are enlarged, the fibers fall through before substantial mixing has taken place, resulting in a nonuniform blend of synthetic and pulp fibers. Furthermore, the resulting mat has a nonuniform mat thickness.
The M & J Web Former has a pulp preparation line and a synthetic fiber preparation line similar to that discussed above for the Dan Web Former. For mixing the wood pulp and synthetic fibers, the M & J Web Former has an enclosed housing with a plurality of rotary props mounted therein. The enclosed housing has a foraminous conveyer belt running therethrough, with a vacuum being drawn beneath the foraminous conveyer. The synthetic fibers and pulp fibers are blown into an upper region of the housing. The rotary propellers or props are suspended from an upper housing wall, and rotate to create turbulence within the housing. This turbulence mixes the incoming synthetic and wood pulp fibers, which are then drawn by the vacuum onto the foraminous belt.
These two known web formers suffer several disadvantages. For example, the Dan Web and M & J Web Formers experience difficulty in producing a mat having a homogeneous blend of synthetic and wood pulp fibers. Furthermore, the Dan Web and M & J Web Formers are not known to enhance the Z tensile strength of the resulting mat. Additionally, the mats produced by these methods are very stiff and have extremely poor drape characteristics. These mats also have an uneven upper surface, resulting in a nonuniform mat thickness. Furthermore, the Dan Web and M & J Web Formers are not understood to vary the hydrophobicity of a mat thereby produced. Also, the Dan Web and M & J Formers have relatively slow mat production line speeds.
A variety of other methods of making limited life pads and other articles are discussed in U.S. Pat. No. 4,900,377 to Redford et al., which is hereby incorporated by reference as to the teachings therein.
Therefore, although other methods and devices have been used for blending cellulosic and synthetic fibers, and other articles have been produced using such methods and devices, a need exists for an improved method, apparatus and article which are directed toward overcoming, and not susceptible to, the above and other limitations and disadvantages.